This invention relates to an optical unit having an optical element such as a diffractive optical element, for example, and, more particularly, to an optical unit suitably usable in the manufacture of a microdevice such as an IC or LSI, for example.
Semiconductor device manufacturing technology has recently been advanced remarkably and, in this trend, microprocessing techniques have been developed significantly. For the microprocessing, reduction projection exposure apparatuses having a resolving power of submicron order and being called steppers are mainly used. For further improvement of resolution, enlargement of the numerical aperture (NA) of an optical system, shortening of exposure wavelength or introduction of a novel optical element has been attempted.
An optical element such as a diffractive optical element may be used in an exposure apparatus for correction of chromatic aberration, for example. On that occasion, among light rays diffracted by the optical element, those light rays (unwanted light) diffracted in directions other than a desired direction or directions may be reflected within a lens barrel, by which ghost or flare may be produced. This may cause non-uniformness of exposure amount distribution upon the surface to be exposed.
It is another object of the present invention to provide an optical instrument having such an optical unit as described above.
It is another object of the present invention to provide an optical instrument having such optical unit as described above.
In accordance with an aspect of the present invention, there is provided an optical unit, comprising: an optical element for deflecting light incident thereon toward different directions; and attenuating means for attenuating light deflected in a predetermined direction, of the different directions.
In accordance with another aspect of the present invention, there is provided an optical unit, comprising: means for holding an optical element being operable to deflect a portion of light incident thereon toward a predetermined direction and having a function that an unwanted light beam in another portion of the light incident thereon is directed in a direction different from the predetermined direction; and attenuating means operable to converge at least a portion of the unwanted light toward a predetermined region through multiple reflection, thereby to attenuate the same.
In one preferred form of these aspects of the present invention, there is cooling means for cooling said attenuating means.
The attenuating means may have a function for converging the light toward a predetermined region through multiple reflection.
The optical element may comprise a diffractive optical element.
The diffractive optical element may have a diffraction pattern formed with a step-like shape.
The light deflected toward the predetermined direction may be a positive first order or negative first order diffraction light of the light deflected by said optical element.
The attenuating means may comprise light absorbing means having a recess of horn-like sectional shape with its inside wall face formed as a reflection surface.
The attenuating means may comprise light absorbing means having a groove-like member with its side face formed as a reflection surface.
The optical element may be fixedly or movably held in a barrel, wherein said attenuating means may be provided over the whole circumference of the inside circumferential surface of said barrel.
The optical unit may have a plurality of light absorbing means.
The cooling means may comprise an air cooling system, a water cooling system, or a Peltier device.
In accordance with a further aspect of the present invention, there is provided an optical instrument having an optical unit as recited above, for projecting light to a photosensitive material through said optical unit.
In accordance with a yet further aspect of the present invention, there is provided an optical instrument having an optical unit as recited above, for projecting light to a photoelectric converting element through said optical unit.
In accordance with a still further aspect of the present invention, there is provided an exposure apparatus, comprising: an illumination optical system; a projection optical system; and an optical unit as recited above, wherein said optical unit is incorporated into one of said illumination optical system and said projection optical system as a portion thereof, so that a predetermined pattern is projected onto a surface to be illuminated, whereby the pattern is printed thereon.
In accordance with a yet further aspect of the present invention, there is provided a device manufacturing method, comprising the steps of: applying a photosensitive material to a wafer; exposing the wafer having the photosensitive material applied thereto, with a device pattern by use of an exposure apparatus; and developing the exposed wafer.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.